Examples of the super-high frequency transmission/reception antenna include a parabolic antenna, a microstrip antenna and a waveguide slot array antenna. Of these, the microstrip array antenna or waveguide slot array antenna is generally used for the purpose of miniaturization by size reduction.
A microstrip array antenna has a microstrip patch array structure using a dielectric substrate which, however, has its characteristic dielectric loss factor to cause substantial signal loss during transmission or reception, and a conductor resistance to add loss with the total loss loss becoming larger as the frequency becomes higher. The use of microstrip array antenna is, therefore, not favoured in the superhigh frequency band.
The waveguide slot array antenna has a typical waveguide structure formed with slot-like holes using no dielectric substrate or the like. Prior art examples related to such a waveguide slot array antenna include Korean patent application No. 2006-0018147 (titled “Multilayer Slot Array Antenna,” applicant: Motonix, Inc., inventors: Cho, Tae Kwan et al., filing date: Feb. 24, 2006), and Korean patent application No. 2007-7000182 (titled “Planar Antenna Module, Triplate Planar Array Antenna, And Triplate Line-waveguide Converter,” applicant: Hitachi Chemical Co., Ltd., inventors: Oota Masahiko, et al., filing date: Jan. 4, 2007).
A type of high-pass filter, waveguide is generally a hollow metal tube with its internal mode having a certain cutoff wavelength, and its fundamental mode being determined by the size of the waveguide. In microwave transmission line, waveguides have been preferred for the advantageous small attenuation over parallel two-wire lines, a coaxial cable or the like, and they have been mainly used for a high output. Waveguides, having various cross-sectional shapes, may be classified into circular waveguide, square waveguide, elliptical waveguide, etc. For the state of the art mobile communication system like the next-generation 5G system, emerging technologies utilize millimeter waves which measure millimeters in wavelength and assume such frequency as 28 GHz or 60 GHz. Multilateral technologies are currently studied for higher performance implementation as well as higher efficiency implementation of various waveguide type devices suitable for processing the millimeter wave signals, for example, a filter or a power distributor, and the like.
In order to realize an arbitrary linearly polarized wave or linear polarization with a typical array antenna, a basic element could be rotated in the same manner as the desired polarization. However, in a waveguide slot array antenna, it is difficult to rotate a single slot because the antenna is structurally integrated with the waveguide that energizes the antenna. This means that the typical antenna is structured not to allow for the polarization to be variably adjusted in practice. Instead, it is usual to rotate the shape of the slot array antenna, but where the shape of a specific antenna is limited, it is difficult to maintain arbitrary polarization. Prior art related to a waveguide slot array antenna having an arbitrary linear polarization has been disclosed by Korean patent application No. 2006-0046075 (titled: “Waveguide Slot Array Antenna For Receiving Random Polarized Satellite Signal,” applicant: Wiworld Co., Ltd., inventor: Park Chan-goo, filing date: May 23, 2006), and Korean patent application No. 2010-0095624 (titled: “A Series Slot Array Antenna,” applicant: Seoul National University R&DB Foundation et al., inventors: Kim, Dong Yeon, et al., filing date: Sep. 30, 2010).